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A survey of parallel execution strategies for transitive closure and logic programs
 DISTRIBUTED AND PARALLEL DATABASES
, 1993
"... An important feature of database technology of the nineties is the use of parallelism for speeding up the execution of complex queries. This technology is being tested in several experimental database architectures and a few commercial systems for conventional selectprojectjoin queries. In particu ..."
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Cited by 24 (6 self)
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An important feature of database technology of the nineties is the use of parallelism for speeding up the execution of complex queries. This technology is being tested in several experimental database architectures and a few commercial systems for conventional selectprojectjoin queries. In particular, hashbased fragmentation is used to distribute data to disks under the control of different processors in order to perform selections and joins in parallel. With the development of new query languages, and in particular with the definition of transitive closure queries and of more general logic programming queries, the new dimension of recursion has been added to query processing. Recursive queries are complex; at the same time, their regular structure is particularly suited for parallel execution, and parallelism may give a high efficiency gain. We survey the approaches to parallel execution of recursive queries that have been presented in the recent literature. We observe that research on parallel execution of recursive queries is separated into two distinct subareas, one focused on the transitive closure of Relational Algebra expressions, the other one focused on optimization of more general Datalog queries. Though the subareas seem radically different because of the approach and formalism used, they have many common features. This is not surprising, because most typical Datalog queries can be solved by means of the transitive closure of simple
Data Fragmentation for Parallel Transitive Closure Strategies
 In Proceedings of the IEEE 9th International Conference on Data Engineering
, 1993
"... A topic that is currently inspiring a lot of research is parallel (distributed) computation of transitive closure queries. In [10] the disconnection set approach has been introduced as an effective strategy for such a computation. It involves reformulating a transitive closure query on a relation in ..."
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Cited by 9 (1 self)
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A topic that is currently inspiring a lot of research is parallel (distributed) computation of transitive closure queries. In [10] the disconnection set approach has been introduced as an effective strategy for such a computation. It involves reformulating a transitive closure query on a relation into a number of transitive closure queries on smaller fragments; these queries can then execute independently on the fragments, without need for communication and without computing the same tuples at more than one processor. Now that effective strategies as just mentioned have been developed, the next problem is that of developing adequate data fragmentation strategies for these approaches. This is a difficult problem, but of paramount importance to the success of these approaches. We discuss the issues that influence data fragmentation. We present a number of algorithms, each focusing on one of the important issues. We discuss the pros and cons of the algorithms, and we give some results of ...
Implementation and performance evaluation of a parallel transitive closure algorithm on PRISMA/DB
, 1993
"... This paper describes an experimental performance study of the parallel computation of transitive closure operations on a parallel database system. This work brings two research efforts together. The first is the development of an efficient execution strategy for the parallel computation of path prob ..."
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Cited by 8 (4 self)
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This paper describes an experimental performance study of the parallel computation of transitive closure operations on a parallel database system. This work brings two research efforts together. The first is the development of an efficient execution strategy for the parallel computation of path problems, called the Disconnection Set Approach. The second is the development and implementation of a parallel, mainmemory DBMS, called PRISMA/DB. Here, we report on the implementation of the disconnection set approach on PRISMA/DB, showing how the latter's design allowed us to easily extend the functionality of the system. It is shown that the parallel implementation of the disconnection set approach yields good performance characteristics, and that linear speedup with respect to a special purpose single processor algorithm is achieved. Finally, we describe a number of experiments that show to what extent data fragmentation issues influence the performance of the disconnection set approach. 1...
Parallel Hierarchical Evaluation of Transitive Closure Queries
, 1991
"... This paper presents a new approach to parallel computation of transitive closure queries using a semantic data fragmentation. We assume that tuples of a large base relation denote edges in a graph, which models a transportation network; we propose a fragmentation algorithm which produces the partiti ..."
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Cited by 7 (5 self)
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This paper presents a new approach to parallel computation of transitive closure queries using a semantic data fragmentation. We assume that tuples of a large base relation denote edges in a graph, which models a transportation network; we propose a fragmentation algorithm which produces the partitioning of the base relation into several fragments such that any fragment corresponds to a subgraph. Any two fragments are considered as either adjacent or nonadjacent; two fragments are adjacent when the corresponding subgraphs have a nonempty intersection. One fragment, called highspeed fragment, collects all edges which guarantee maximum speed, these edges correspond to highways or to highspeed intercity trains. Thus, the fragmentation algorithm induces a hierarchical relationship between the highspeed fragment and all other fragments. With this fragmentation, any query about paths connecting two nodes can be answered by using just the fragments in which nodes are located and the high...
A Temporal Paraconsistent Relational Algebra for Incomplete and Inconsistent Information
 In Proceedings of the 33rd ACM Southeast Conference
, 1995
"... We construct a framework for natural handling of incomplete and inconsistent information in temporal databases. Central to this framework are structures that we call timevarying paraconsistent relations, which are essentially 4valued relations that vary over time. For such structures, we present a ..."
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We construct a framework for natural handling of incomplete and inconsistent information in temporal databases. Central to this framework are structures that we call timevarying paraconsistent relations, which are essentially 4valued relations that vary over time. For such structures, we present an algebra based on temporal semantics in which there is no explicit manipulation of time indices, yet it is rich enough to express recursive equations as queries. The algebra is a consistent extension of the relational algebra; it supports basic algebraic equivalences, and has a welldefined formal semantics. We also provide many examples of queries expressed in this algebra. To our knowledge, our framework is the first treatment of inconsistent information in the context of temporal databases. 1 Introduction One limitation of the relational data model of Codd [7] is its lack of applicability to nonclassical situations. These are situations involving incompleteness, or more importantly, eve...
A recursive temporal algebra and temporal completeness
 Proceedings of the Third International Workshop on Temporal Representation and Reasoning (TIME’96
, 1996
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A Temporal Algebra with Recursive Equations
, 1995
"... This paper introduces a recursive temporal algebra for querying timevarying data. The algebra, called ! , is based on a temporal relational data model in which a temporal database is modeled as a collection of timevarying relations. Each timevarying relation is a collection of ordinary relatio ..."
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This paper introduces a recursive temporal algebra for querying timevarying data. The algebra, called ! , is based on a temporal relational data model in which a temporal database is modeled as a collection of timevarying relations. Each timevarying relation is a collection of ordinary relations indexed by moments in time. In ! , recursive queries (such as the transitive closure of a given relation) can be formulated through equations. It is shown that other forms of recursion, such as linear recursion, can also be expressed using iteration through time. The meaning of recursive equations is formulated using a standard approach based on fixedpoint semantics. Temporal completeness of ! with bounded time is established, with respect to two other temporal algebras based on temporal semantics which also offer linear recursive operators. Keywords: Temporal databases, temporal algebras, timevarying relations, recursive queries, recursive equations, fixedpoint semantics, linea...
Formalizing a Broader Recursion Coverage in SQL
"... Abstract. SQL is the de facto standard language for relational databases and has evolved by introducing new resources and expressive capabilities, such as recursive definitions in queries and views. Recursion was included in the SQL99 standard, but this approach is limited as only linear recursion ..."
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Abstract. SQL is the de facto standard language for relational databases and has evolved by introducing new resources and expressive capabilities, such as recursive definitions in queries and views. Recursion was included in the SQL99 standard, but this approach is limited as only linear recursion is allowed, mutual recursion is not supported, and negation cannot be combined with recursion. In this work, we propose a new approach, called RSQL, aimed to overcome these limitations and others, allowing in particular cycles in recursive definitions of graphs and mutually recursive relation definitions. In order to combine recursion and negation, we import ideas from the deductive database field, such as stratified negation, based on the definition of a dependency graph between relations involved in the database. We develop a formal framework using a stratified fixpoint semantics and introduce a proofofconcept implementation.
GraphBased Processing of Logic Programs
"... A lot of practical recursive logic queries to a deductive database are expressed by linear recursive datalog programs with exactly one recursive rule, socalled linear sirups. We give a characterization of ksided linear datalog sirups  the concept was introduced by Naughton in [Na 87]  based on ..."
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A lot of practical recursive logic queries to a deductive database are expressed by linear recursive datalog programs with exactly one recursive rule, socalled linear sirups. We give a characterization of ksided linear datalog sirups  the concept was introduced by Naughton in [Na 87]  based on a graph model and present a normal form to which every linear datalog sirup can be transformed. Normalized linear datalog sirups can be decomposed by a counting technique into k lowerdimensional linear sirups which can be evaluated in parallel by very efficient query evaluation algorithms. For certain sets of linear sirups defining the same intensional predicate we can also derive a decomposition approach from the graph model. Another technique based on the prefixes of compiled expansions transforms a set of chain rules with binary predicate symbols, a socalled CFG program, into a transition graph. Common subexpressions between different compiled formulas can be detected by the graph min...